FIG. 1 is a cross sectional view of a conventional optical signal receiver module to be used for optical signal transmission via an optical fiber. As shown in FIG. 1, a light receiver unit 2 having a light receiver element 4 is fixed to a receptacle 1. The light receiver element 4 receives an input optical signal and converts it into an electric signal. The light receiver element 4 outputs the electric signal via a lead wire 6 to an amplifier unit 3. The amplifier unit 3 amplifies the electric signal received from the light receiver element 4 by an amplifier element 5 and outputs the amplified signal.
In assembly, the angle of the light receiver unit 2 is adjusted so that the light reception optical axis of the receptacle 1 aligns with the optical axis of the light receiver element 4. After angle adjustment, the light receiver unit 2 is fixedly mounted in the receptacle 1. The lead wire 6 extends out of the light receiver unit 2, generally perpendicular to the surface of the light receiver unit 2 opposite to the mounting surface of the light receiver element 4 on a substrate 2a. The amplifier unit 3 is therefore mounted generally parallel with the lead wire 6, i.e., generally parallel with the optical axis of incident light to the receptacle 1.
For the light receiver unit 2 whose optical axis is aligned with the receptacle 1, a common cylindrical member can be used and selected from general inexpensive package components. Therefore, a product can be made compact with excellent manufacturing operability. However, the light receiver unit 2 and amplifier unit 3 are mounted spaced apart from each other. Therefore, the lead wire 6 interconnecting both the units becomes long, and so stray capacitance increases. An output signal from the light receiver unit 2 is generally very small. As a result, it is susceptible to external noises, resulting in a poor S/N ratio. The input capacitance of the amplifier unit 3 also increases, degrading the frequency characteristic. Furthermore, the outer dimension of the module is long in the optical axis direction of incident light, imposing a limit in compacting the module.
FIG. 2 is a cross sectional view of another conventional light receiver module. As seen from FIG. 2, an amplifier element 5 together with a light receiver element 4 is packaged within a light receiver unit 2. In assembly, the light receiver unit 2 is first formed, and then fixed to a receptacle 1 with the optical axes of the receptacle 1 and light receiver element 4 being aligned with each other.
In the module shown in FIG. 2, the light receiver element 4 and amplifier element 5 are housed within the same package, making the interconnection therebetween as short as possible. As a result, this module is resistant to external noises, and the frequency characteristic can be effectively improved. However, the shape of the light receiver unit 2 is not of a general shape but is a specific shape. Namely, the light receiver unit 2 cannot use a generally cylindrical member commonly used, resulting in expensive package components. Components of such a specific shape also require specific mounting jigs, posing some manufacturing problems. The dimension of the module becomes long in the direction perpendicular to the optical axis of the receptacle, imposing a limit in compacting the module.
As described above, the conventional optical signal receiver modules have the following problems. The dimension of the module becomes long in the optical axis direction of the receptacle 1 or in the direction perpendicular to the optical axis, imposing a limit in compacting the module. It is also difficult to improve productivity, reduce cost, and improve the S/N ratio and frequency characteristic of such modules.